There is generally a growing interest in making more cost effective lighting devices with health benefits. Light sources producing artificial white light are being adopted at a high rate. Such light sources can produce high quality light with a color rendering index (CRI) beyond 90 with very high efficiencies. However, one of the problems of such light sources as compared with sun light is the absence of certain parts of the spectrum which have specific benefits to humans beyond providing visible light. For example, ultra violet (UV) light (albeit at very low intensities) is very important for production of vitamin D (or for crispy white light, skin tanning, disinfection, insect attraction, skin treatment, etc.). For this purpose, it is desired to introduce UV LEDs in combination with white and/or colored LEDs in lighting devices. UV LEDs produce normally light in the wavelength range of 200 nm to 400 nm. For production of vitamin D, the wavelength is normally in the range of 280 nm to 320 nm.
Chip on Board (CoB) relates to a process technology which is increasingly used for producing light sources. The CoB is basically a light source of multiple LED chips bonded directly to a substrate forming a single module. The cost effectiveness and efficiency of these light sources are making them very attractive. It may therefore be interesting to combine CoB with one or more UV light sources.
In general, there is a need for providing a lighting device with the above benefits of UV light and an improved lifetime.
US2004/145312 A1 discloses a light source which includes an LED that emits excitation light, a first flexible multilayer reflector that reflects at least a portion of visible light and transmits the excitation light, and a layer of phosphor material adjacent the flexible multilayer reflector. The phosphor material emits visible light when illuminated with the excitation light